The present invention relates generally to workholders or work platforms and more particularly to work platforms that are rotatably positioned to manipulate the position of a work piece.
During manual fabrication of parts and components in manufacturing operations, operators are often required to handle and manipulate the parts and components, hereinafter referred to as work pieces, along with associated tooling, in order to perform work on the work piece. For example, in the fabrication of composite parts for aircraft structures, individual composite plies are layed-up over metal bond jigs to form the geometry of the structure. The metal bond jigs vary widely in shape and size, and bond jigs for smaller parts such as wing ribs and fuselage frames that may be manually manipulated generally range between approximately one (1) and twenty five (25) pounds. After the composite plies are cured over the bond jigs, the plies are generally trimmed to a final shape for further assembly operations.
During lay-up and trim operations, an operator frequently picks up and handles the bond jig and accordingly, many operators suffer musculoskeletal problems due to sustained handling during both lay-up of the composite plies and trimming of the composite plies after cure. Known musculoskeletal problems include muscle, tendon, ligament, blood vessel, and nerve damage, along with carpal tunnel syndrome, epicondylitis, and rotator cuff tendonitis. Additionally, many operators cut and injure themselves during trimming operations when one hand is being used to hold the bond jig and the other hand is used to trim the plies. Further, many operators forego the use of mandatory cotton work gloves in order to achieve a better handle on the bond jig and work piece. As a result, injuries to the operators occur and the costs of manufacturing operations increase dramatically.
Devices are known in the art for holding work pieces, often referred to as workholders, which are available in a variety of configurations depending on the work piece to be manipulated. For example, U.S. Pat. No. 5,738,344 to Hagman discloses an ergonomic work piece positioner that includes a relatively complicated system of springs that are controlled by a fluid source, which also acts upon a piston that holds and releases the position of a work piece. Generally, the work piece is secured to the positioner using a threaded arm, wherein the work piece is threaded onto the positioner. Similarly, U.S. Pat. No. 5,314,174, also to Hagman, discloses a spring pneumatic control system, wherein a pneumatic source holds and releases the position of a work piece. Unfortunately, the positioners are relatively complicated and require the use of a foot pedal to activate a control system rather than manipulating the work piece by hand. Further, installation and removal of the work piece is relatively time consuming.
Additional workholders are commercially available and include ball joint devices, wherein the ball joint generally rotates 360xc2x0 and pivots 90xc2x0 to position a work piece. The ball joint devices generally comprise a slot, or a knob that controls a split ball, to limit the position of the ball joint, along with a lever to reposition the work as necessary. Therefore, the work piece is manipulated using a mechanical lever, which is positioned a distance away from the center of gravity of the work piece. As a result, a moment is created between the lever and the work piece when the work piece is manipulated by an operator, which may cause an awkward force to manipulate heavier work pieces. Further, the work piece is secured to the workholder using mechanical fasteners, which results in additional time to secure and remove the work piece from the workholder.
Accordingly, there remains a need in the art for a relatively simple and cost effective device to manipulate the position of a work piece, wherein handling by an operator is minimized. Further, the device should provide for ease of securing and removing a work piece to and from the device to facilitate more efficient manufacturing operations.
In one preferred form, the present invention provides a swivel-base work platform that comprises a hemisphere unit rotatably disposed within a base unit, wherein a hard-stop disk disposed at a lower portion of the hemisphere unit limits the rotation of the hemisphere unit by engaging the base unit. Further, the hemisphere unit comprises a work surface disposed at an upper portion thereof, and thus a work piece, such as a part and/or a tool, may be secured to the work surface and manipulated as desired by an operator.
The base unit further comprises a hemisphere cradle that defines a concave inner surface and an aperture. Accordingly, the hemisphere unit is disposed within the aperture, wherein a convex surface of the hemisphere unit engages the concave inner surface of the hemisphere cradle, thereby allowing the hemisphere unit to rotate within the base unit. Further, the hard-stop disk engages a lower surface of the hemisphere cradle to limit the position of the hemisphere unit and thus the work piece. With a larger hard-stop disk, the range of motion of the hemisphere unit decreases, while a smaller hard-stop disk increases the range of motion of the hemisphere unit. Accordingly, the size of the hard-stop disk may be adjusted for the desired range of motion. Moreover, the shape of the hard-stop disk may be circular or rectangular, among other shapes, to further limit the range of motion of the work piece.
Furthermore, the base unit preferably comprises a base plate spaced apart from the hemisphere cradle and a plurality of support legs secured between the hemisphere cradle and the base plate. Accordingly, the support legs provide a space between the hemisphere cradle and the base plate, thereby providing access to the lower portion of the hemisphere unit, the hard-stop disk, and the vacuum line if applicable. Moreover, the base plate provides for a mobile configuration such that the swivel-base work platform may be used at a variety of work stations throughout a manufacturing facility.
Preferably, a vacuum source is used to secure the work piece to the work surface. Accordingly, the hemisphere unit, the work surface, and the hard-stop disk further comprise concentric apertures, wherein a vacuum line is disposed therethrough. The end of the vacuum line is disposed proximate the work surface at a vacuum port and thus the work piece is secured to the work surface by vacuum at the vacuum port. Additionally, a swivel fitting is preferably employed at the end of the vacuum line proximate the work surface so that the hemisphere unit may be rotatably disposed independent of the vacuum line and further to prevent twisting of the vacuum line.
Alternately, additional attachment devices other than a vacuum source may be used such as a magnetic source, cam or screw clamping, positioning pins, or restraining fences, among others. Accordingly, the reference to a vacuum source to secure the work piece shall not be construed as limiting the scope of the present invention.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.